1. Technical Field
The present invention relates to a solid state imaging device and an image acquisition method.
2. Related Art
In the related art, it has been known that, when light is applied to a semiconductor layer in which semiconductors having different types of carriers are connected, photovoltaic currents can be acquired due to the excitation of photoelectrons (internal photoelectric effect). A solid state imaging element, which is a semiconductor image sensor, is provided as an element which uses the effect.
Although the solid state imaging element is widely used for a digital image input device which is represented by a digital scanner, a digital camera, or the like, it has been known that an area (dynamic range) in which incident light can be detected is narrow and a range in which an excellent image can be acquired for a certain quantity of light, that is, an exposure time is narrow, compared to a silver salt film which is used for analog photography or the like. Here, there is a method of acquiring a plurality of pieces of image information for respective different exposure times. According to the method, an image is formed by merging the plurality of pieces of image information.
In addition, a method of setting two types of pixels which have different sensitivities to a group and separately reading the electric charge signals of the pixels in each group (for example, refer to JP-A-04-298175) is proposed as a method capable of forming an image without merging the plurality of pieces of image information. A solid state imaging device in which the center of the geometric shape of a light receiving element is shifted in a row direction and a column direction by half of pitch, a so-called a honeycomb arrangement, has been proposed (for example, refer to JP-A-2000-125209).
However, in the method of acquiring the plurality of pieces of image information for the respective different exposure times, the pieces of image information at different imaging timings are merged, and thus there is a possibility that positional displacement may occur in the formed image.
In addition, in the method disclosed in JP-A-04-298175, two types of pixels having different light sensitivities are mixed, with the result that only the pixels corresponding to half of the number of total pixels can be arranged, and thus there are problems in that it is difficult to secure a sufficient quantity of light and it is difficult to perform imaging with high sensitivity.
Further, in the apparatus disclosed in JP-A-2000-125209, an effective pixel area is reduced due to a wall member or the like which realizes a honeycomb arrangement, and thus it is difficult to secure a sufficient quantity of light and it is difficult to perform imaging with high sensitivity.
Such problems similarly exist in a solid state imaging device which includes the solid state imaging element using the internal photoelectric effect and an image acquisition method which uses the solid state imaging device in addition to the method disclosed in JP-A-04-298175 or the apparatus disclosed in JP-A-2000-125209.